1. Field of the Invention
The present invention relates to a double-side image forming apparatus and a double-side image forming method for forming images on both surfaces of each recording medium on the basis of image data.
2. Description of the Related Art
In the related art, there has been known a double-side image forming apparatus including a storage unit for storing image data, an image forming unit, and a transporting unit. The image forming unit forms an image on a recording medium (such as a sheet of paper or a film) transported in a predetermined direction, on the basis of image data stored in the storage unit. The transporting unit transports the recording medium in the predetermined direction relative to the image forming unit. In order to form images on both surfaces of the recording medium, the following processes are performed. An image is formed on a front surface of the recording medium. Then, the recording medium is turned upside down to change a downstream side end of the recording medium during the formation of the image to an upstream side end viewed from the transporting direction of the recording medium. The recording medium is transported in the predetermined direction relative to the image forming unit again to form an image on a rear surface of the recording medium. The recording medium is successively stacked on a paper outlet tray.
In this type double-side image forming apparatus, it is preferable that a larger number of images can be formed on recording media continuously and that recording media discharged to a paper outlet tray can be bound together while stacked on the paper outlet tray as they are discharged.
For example, the way of binding a plurality of recording media in sides parallel to the transporting direction of the recording media or the way of binding a plurality of recording media in sides perpendicular to the transporting direction of the recording media may be used for binding the plurality of recording media after the formation of images. In either case, it is preferable that images appear in a predetermined direction without inversion when a user reads the recording media by turning the pages of the recording media one by one.
In this type double-side image forming apparatus, the transporting direction of each recording medium is however reversed (the recording medium is transported while the downstream side end of the recording medium during the formation of an image on the front surface of the recording medium is changed to an upstream side end viewed from the transporting direction of the recording medium) when an image is formed on the rear surface of the recording medium. Accordingly, if recording media stacked on the paper outlet tray are bound in sides parallel to the transporting direction of the recording media while the recording media are stacked, there arises a so-called inversion phenomenon that inverted images appear on alternate pages when the user reads images on the recording media by turning the pages one by one.
As an apparatus to prevent the inversion phenomenon, there has been known an apparatus in which image data stored in a memory, which is a storage unit, before formation of images on recording media are inverted in terms of data sequence on alternate pages so that image data not-inverted and image data inverted are used alternately for forming images on the recording media (e.g., JP-A-Hei. 10-166544 (pages 7-8; and FIGS. 4-10)).
On the other hand, the capacity of the memory for storing image data limits number of documents allowed to be used for forming images on recording media continuously. In consideration of the limitation, there has also been known an apparatus in which image data are compressed and stored as compressed data in the memory, and the compressed data are read from the memory and expanded at the time of formation of images so that the number of documents allowed to be used for forming images continuously can be increased while the amount of memory consumption per document page can be suppressed (e.g., JP-A-2001-223884(page 29; and FIG. 41).
According to the apparatus disclosed in JP-A-Hei. 10-166544, there is however a problem that the capacity of the memory limits the number of documents allowed to be used for forming images continuously because the apparatus has no compression unit by which the capacity of the memory to be used can be reduced when image data are stored in the memory.
According to the apparatus disclosed in JP-A-2001-223884, there is a problem that the time required for forming images is prolonged because data processing must be carried out for expanding and inverting compressed data in terms of data sequence on alternate pages to prevent the inversion phenomenon when images are formed on recording media.